Humans exhibit severe capacity limits: one can hardly keep in mind more than 3 or 4 items, or perform more than one task at a time. The goal of this research proposal is to develop using neuroimaging tools an understanding of the central mechanisms that limit our ability to multi-task. Since dual-tasking interference results from the failure of two sensori-motor channels to process information independently, this research will map out the neural flow of information in sensorimotor tasks that do not overlap in either sensory input or motor output. Other studies will specifically target the stage of response selection along this information pathway since it is the cognitive process most often associated with dual-task limitation. Novel fMRI chronometric approaches will be used to isolate brain regions involved in response selection, and to determine their role along the information pathway. In addition, these studies will assess whether there are both task-specific and general-purpose response-selection substrates. The establishment of the neural information pathways will serve as the groundwork for the dual-task interference studies, which will test for brain activity correlated with dual-task costs under conditions that are not affected by instructions or task demands. The hypothesis that activity in response selection ROIs will be negatively correlated with performance improvement during practice will be rigorously tested. fMRI chronometric studies will also be carded out to determine whether the capacity-limited process corresponds to a serial bottleneck that can only process one response selection at a time, or whether it can process two tasks simultaneously but divides the resources between these tasks (graded sharing model). Finally, given recent findings that perceptual and response processing demands interact, fMRI studies will address whether there is a single general-purpose capacity limited process or distinct but interacting perceptual and response capacity limits. In addition, this project will investigate how response selection demands affect perception by determining whether our inability at doing more than one task at a time affects our visual cortex ability to "see".